As a process for producing an L-amino acid, particularly L-glutamine, by a fermentation method, many methods using a coryneform bacterium are known. Examples of such process for producing L-glutamine include a method using a coryneform bacterium imparted with azaserine resistance (patent document 1), a method using coryneform bacterium imparted with 6-diazo-5-oxo-norleucine resistance (patent document 2) and the like.
In addition, as a process for producing L-glutamine using a coryneform bacterium with enhanced glutamine synthetase activity, a method using a coryneform bacterium showing a decreased activity of glutamine synthetase adenylyltransferase which controls a glutamine synthetase via adenylylation (non-patent document 1, patent document 3), a method using a coryneform bacterium wherein the 405th amino acid residue in the ORF of glutamine synthetase that is subject to adenylylation by glutamine synthetase adenylyl transferase is substituted (non-patent document 1, patent document 4) and a, method using a coryneform bacterium in which an activity of PII protein is decreased (non-patent document 2, patent document 3) and the like are known.
As a process for producing L-glutamine by using Escherichia coli, only a method using Escherichia coli having a glutamine synthetase without an adenylylation ability has been reported (patent document 4).
It has been reported that YeiG encoded by yeiG gene in Escherichia coli has a serine esterase motif and has a carboxylesterase activity (non-patent document 3). Also, it has been suggested that it acts in a glutathione-dependent formaldehyde detoxification pathway since it has a high hydrolyzing activity against formylglutathione.
The expression of formylglutathione hydrolase encoded by the frmB (yaiM) gene of Escherichia coli is induced by the presence of formaldehyde in the medium (non-patent document 3). However, since YeiG is constitutively expressed even in the absence of formaldehyde in the medium, it may have an unknown function.
A process for producing L-glutamine, which uses a microorganism highly expressing YeiG, is not known, and whether YeiG is involved in the amino acid synthesis and what influence the high expression of YeiG exerts on the amino acid synthesis are not known.